Dominant mutations affecting both sporulation and sterigmatocystin biosynthesis in Aspergillus nidulans

The initiation of conidiophore development in the filamentous fungus Aspergillus nidulans is a complex process requiring the activities of several genes including fluG, flbA, flbB, flbC, flbD, and flbE. Recessive mutations in any one of these genes result in greatly reduced expression of the brlA developmental regulatory gene and a colony morphology described as fluffy. These fluffy mutants have somewhat diverse phenotypes but generally grow as undifferentiated masses of vegetative hyphae to form large cotton-like colonies. In this paper we describe a genetic screen to identify dominant mutations resulting in similar fluffy colony morphologies. We have identified 36 dominant fluffy mutant strains and shown that 29 of these mutants have greatly reduced brlA expression as compared to wild-type. In addition, we have found that 19 of these mutants are not only developmentally altered but also fail to produce the toxic, carcinogenic, secondary metabolite sterigmatocystin. At least three of the mutants isolated result from dominant activating mutations in fadA which encodes the G alpha subunit of a heterotrimeric G-protein. Another of the mutants results from a dominant interfering mutation in brlA. We discuss the approaches taken to characterize these potentially important regulators of growth, development and secondary metabolism.

Aspergillus sporulation and mycotoxin production both require inactivation of the FadA G alpha protein-dependent signaling pathway

The filamentous fungus Aspergillus nidulans contains a cluster of 25 genes that encode enzymes required to synthesize a toxic and carcinogenic secondary metabolite called sterigmatocystin (ST), a precursor of the better known fungal toxin aflatoxin (AF). One ST Cluster (stc) gene, aflR, functions as a pathway-specific transcriptional regulator for activation of other genes in the ST pathway. However, the mechanisms controlling activation of aflR and synthesis of ST and AF are not understood. Here we show that one important level for control of stc gene expression requires genes that were first identified as early acting regulators of asexual sporulation. Specifically, we found that loss-of-function mutations in flbA, which encodes a RGS domain protein, or dominant activating mutations in fadA, which encodes the alpha subunit of a heterotrimeric G protein, block both ST production and asexual sporulation. Moreover, overexpression of flbA or dominant interfering fadA mutations cause precocious stc gene expression and ST accumulation, as well as unscheduled sporulation. The requirement for flbA in sporulation and ST production could be suppressed by loss-of-function fadA mutations. The ability of flbA to activate stc gene expression was dependent upon another early acting developmental regulator, fluG, and AflR, the stc gene-specific transcription factor. These results are consistent with a model in which both asexual sporulation and ST production require inactivation of proliferative growth through inhibition of FadA-dependent signaling. This regulatory mechanism is conserved in AF-producing fungi and could therefore provide a means of controlling AF contamination.

beta-Agarase from Pseudomonas sp. W7: purification of the recombinant enzyme from Escherichia coli and the effects of salt on its activity

The recombinant plasmid (pJAI), harbouring the agarase gene (pjaA) of Pseudomonas sp. W7, was introduced and expressed in Escherichia coli JM83. The agarase was purified using a combination of acetone precipitation and anion-exchange, gel-filtration and affinity chromatographies, with overall yield of 10% from the culture supernatant of E. coli JM83 (pJAI). The purified agarase migrated as a single band (molecular mass 59 kDa) on SDS/PAGE and was found to be beta-agarase, which could hydrolyse the beta-1,4 linkage of agarose to yield neoagarotetraose as the main product. Optimal enzyme activity was at pH 7.8 and the temperature optimum spanned the broad range 20-40 degrees C. The recombinant agarase was halophilic, maximum activity being exhibited at 0.9 M NaCl. This halophilic property could improve the production of neoagaro-oligosaccharides available in a marine environment.

Nucleotide sequence of the vmhA gene encoding hemolysin from Vibrio mimicus

The structural gene (vmhA) of hemolysin from Vibrio mimicus (ATCC33653) was cloned and sequenced. The vmhA gene contains an open reading frame consisting of 2232 nucleotides which can code for a protein of 744 amino acids with a predicted molecular mass of 83,059. The similarity of amino acid sequence shows 81.6% identity with Vibrio cholerae El Tor hemolysin.

The Aspergillus FlbA RGS domain protein antagonizes G protein signaling to block proliferation and allow development

flbA encodes an Aspergillus nidulans RGS (regulator of G protein signaling) domain protein that is required for control of mycelial proliferation and activation of asexual sporulation. We identified a dominant mutation in a second gene, fadA, that resulted in a very similar phenotype to flbA loss-of-function mutants. Analysis of fadA showed that it encodes the alpha-subunit of a heterotrimeric G protein, and the dominant phenotype resulted from conversion of glycine 42 to arginine (fadA(G42R)). This mutation is predicted to result in a loss of intrinsic GTPase activity leading to constitutive signaling, indicating that activation of this pathway leads to proliferation and blocks sporulation. By contrast, a fadA deletion and a fadA dominant-interfering mutation (fadA(G203R)) resulted in reduced growth without impairing sporulation. In fact, the fadA(G203R) mutant was a hyperactive asexual sporulator and produced elaborate sporulation structures, called conidiophores, under environmental conditions that blocked wild-type sporulation. Both the fadA(G203R) and the fadA deletion mutations suppressed the flbA mutant phenotype as predicted if the primary role of FlbA in sporulation is in blocking activation of FadA signaling. Because overexpression of flbA could not suppress the fadA(G42R) mutant phenotype, we propose that FlbA's role in modulating the FadA proliferation signal is dependent upon the intrinsic GTPase activity of wild-type FadA.

Specific domains of beta-amyloid from Alzheimer plaque elicit neuron killing in human microglia

Alzheimer's disease (AD) is found to have striking brain inflammation characterized by clusters of reactive microglia that surround senile plaques. A recent study has shown that microglia placed in contact with isolated plaque fragments release neurotoxins. To explore further this process of immunoactivation in AD, we fractionated plaque proteins and tested for the ability to stimulate microglia. Three plaque-derived fractions, each containing full-length native A beta 1-40 or A beta 1-42 peptides, elicited neurotoxin release from microglia. Screening of various synthetic peptides (A beta 1-16, A beta 1-28, A beta 12-28, A beta 25-35, A beta 17-43, A beta 1-40, and A beta 1-42) confirmed that microglia killed neurons only after exposure to nanomolar concentrations of human A beta 1-40 or human A beta 1-42, whereas the rodent A beta 1-40 (5Arg-->Gly, 10Tyr-->Phe 13His-->Arg) was not active. These findings suggested that specific portions of human A beta were necessary for microglia-plaque interactions. When coupled to microspheres, N-terminal portions of human A beta (A beta 1-16, A beta 1-28, A beta 12-28) provided anchoring sites for microglial adherence whereas C-terminal regions did not. Although itself not toxic, the 10-16 domain of human A beta was necessary for both microglial binding and activation. Peptide blockade of microglia-plaque interactions that occur in AD might prevent the immune-driven injury to neurons.

Conservation of structure and function of the aflatoxin regulatory gene aflR from Aspergillus nidulans and A. flavus

Under limiting growth conditions, Aspergillus nidulans produces a carcinogenic secondary metabolite related to aflatoxin and called sterigmatocystin (ST). The genes for ST biosynthesis are co-ordinately regulated and are all found within an approximately 60-kilobase segment of DNA. One of the genes within this region is predicted to encode a CX2CX6CX6CX2CX6CX2 zinc binuclear cluster DNA-binding protein that is related to the Aspergillus flavus and Aspergillus parasiticus aflatoxin regulatory gene aflR. Deletion of the A. nidulans aflR homolog resulted in an inability to induce expression of genes within the ST gene cluster and a loss of ST production. Because A. nidulans aflR mRNA accumulates specifically under conditions that favor ST production we expect that activation of ST biosynthetic genes is determined by A. nidulans aflR. In support of this hypothesis, we demonstrated that induced expression of the A. flavus aflR gene in A. nidulans, under conditions that normally suppress ST gene expression, resulted in activation of genes in the ST biosynthetic pathway. This result demonstrates that AflR function is conserved between Aspergillus spp. and that aflR expression is sufficient to activate genes in the ST pathway.

Excimer laser photorefractive keratectomy for myopia

To evaluate the safety, effectiveness and stability of excimer laser photorefractive keratectomy (PRK) treatment, we studied its posttreatment results in 44 normal-sighted myopic eyes where a 193-nm emission wavelength excimer laser was used to correct myopia. The eyes were divided into three groups according to the preoperative refractive error and attempted correction: group I, preoperative myopia < or = 6.00 diopters (D), full correction; group II, preoperative myopia between 6.00 and 8.00 D, full correction; group III, preoperative myopia > 8.00 D, attempted correction of 8.00 D. Percentages of relative spherical equivalents (ie, observed spherical equivalent -- expected spherical equivalent) within +/- 1.0 D 3 months after treatment were 95% in group I, 64% in group II and 67% in group III. Uncorrected visual acuity of 20/40, or better, was achieved in 100% of eyes in group I, and 92% in group II at 6 months. Initial overcorrection followed by myopic regression was observed in all groups. The refractive outcome in our study was stable 3 months after surgery. Anterior stromal haze was mild and disappeared gradually 3 months postoperatively. The greater the diopter correction needed, the higher the grade of corneal haze (p < 0.01). There were no significant complications. The results of this study demonstrated that excimer laser PRK appears to be a reasonably predictable and stable procedure to correct low to moderate myopia.

Twenty-five coregulated transcripts define a sterigmatocystin gene cluster in Aspergillus nidulans

Sterigmatocystin (ST) and the aflatoxins (AFs), related fungal secondary metabolites, are among the most toxic, mutagenic, and carcinogenic natural products known. The ST biosynthetic pathway in Aspergillus nidulans is estimated to involve at least 15 enzymatic activities, while certain Aspergillus parasiticus, Aspergillus flavus, and Aspergillus nomius strains contain additional activities that convert ST to AF. We have characterized a 60-kb region in the A. nidulans genome and find it contains many, if not all, of the genes needed for ST biosynthesis. This region includes verA, a structural gene previously shown to be required for ST biosynthesis, and 24 additional closely spaced transcripts ranging in size from 0.6 to 7.2 kb that are coordinately induced only under ST-producing conditions. Each end of this gene cluster is demarcated by transcripts that are expressed under both ST-inducing and non-ST-inducing conditions. Deduced polypeptide sequences of regions within this cluster had a high percentage of identity with enzymes that have activities predicted for ST/AF biosynthesis, including a polyketide synthase, a fatty acid synthase (alpha and beta subunits), five monooxygenases, four dehydrogenases, an esterase, an 0-methyltransferase, a reductase, an oxidase, and a zinc cluster DNA binding protein. A revised system for naming the genes of the ST pathway is presented.

Genetic mapping indicates that VP4 is the rotavirus cell attachment protein in vitro and in vivo

To identify the rotavirus protein which mediates attachment to cells in culture, viral reassortants between the simian rotavirus strain RRV and the murine strains EHP and EW or between the simian strain SA-11 and the human strain DS-1 were isolated. These parental strains differ in the requirement for sialic acid to bind and infect cells in culture. Infectivity and binding assays with the parental and reassortant rotaviruses indicate that gene 4 encodes the rotavirus protein which mediates attachment to cells in culture for both sialic acid-dependent and -independent strains. Using ligated intestinal segments of newborn mice and reassortants obtained between the murine strain EW and RRV, we developed an in vivo infectivity assay. In this system, the infectivity of EW was not affected by prior treatment of the enterocytes with neuraminidase, while neuraminidase treatment reduced the infectivity of a reassortant carrying gene 4 from RRV on an EW background more than 80% relative to the controls. Thus, VP4 appears to function as the cell attachment protein in vivo as well as in vitro.

Cloning of a novel crystal protein gene cry1K from Bacillus thuringiensis subsp. morrisoni

A novel crystal protein gene cry1K has been cloned and sequenced from a Bacillus thuringiensis subsp. morrisoni BF190 isolated from phylloplane. The upstream promoter region of cry1K was almost identical with that of cry1B. The deduced amino acid sequence of Cry1K contains 1215 amino acid residues with an estimated molecular mass of 137 kDa. Comparison of the amino acid sequence of the Cry1K with that of Cry proteins revealed that Cry1K is most closely related to Cry1B and Cry1I. Cry1K has a high degree of identity with Cry1B in the region between initiator codon and conserved sequence block 1, and with Cry1F in the region between conserved block 3 and 5. Protein inclusion purified from a recombinant strain of B. thuringiensis expressing the cry1K gene was found to have a different insect-host specificity from Cry1B, Cry1I and Cry1F, Cry1K was found to be selectively toxic to Artogeia rapae and not active to Plutella xylostella.

Insulin secretory defect in Zucker fa/fa rats is improved by ameliorating insulin resistance

The role of insulin resistance in the impaired glucose-stimulated insulin release of Zucker fatty rats was investigated using the insulin-sensitizing thiazolidinedione drug pioglitazone. Fatty rats had fasting hyperinsulinemia yet a blunted secretory response to intravenous glucose compared with lean age-matched controls. Islets from fatty rats secreted less insulin (based on islet DNA) in response to high glucose than islets from lean rats but secreted normal amounts of insulin when tolbutamide or alpha-ketoisocaproic acid (alpha-KIC) was the stimulus. Administering pioglitazone for 9 days diminished basal hyperinsulinemia and increased the insulin response to high glucose by fatty rats but not by lean controls. Pioglitazone pretreatment augmented the secretory response by isolated islets to high glucose, alpha-KIC, and tolbutamide. Augmentation of islet insulin release was not associated with reduced plasma glucose concentration, suggesting that altered glycemia was not involved. Pancreas and islet insulin content was greater in fatty rats than in lean controls and was decreased by pioglitazone; hence, insulin stores and glucose-stimulated insulin release did not correlate. Pioglitazone treatment did not affect the rate of islet glucose usage or ATP/ADP in the presence of 2.75 or 16 mmol/l glucose. These data indicate that ameliorating insulin resistance reverses defective glucose-stimulated insulin release by Zucker fa/fa rats. After pioglitazone administration, insulin secretion may be augmented by increased generation of a metabolic coupling factor from glucose or at a later step in the secretory process that is common to both glucose and nonglucose secretagogues.

Sterigmatocystin biosynthesis in Aspergillus nidulans requires a novel type I polyketide synthase

A filamentous fungus, Aspergillus nidulans, produces the carcinogenic mycotoxin sterigmatocystin (ST), which is a polyketide-derived secondary metabolite. A gene (pksST) encoding the ST polyketide synthase (PKSst) in A. nidulans was cloned, sequenced, and characterized. Large induced deletion mutants, which did not make ST or any ST intermediates, were used to identify genes associated with ST biosynthesis. Among the transcripts detected within the deletion region, which showed developmental expression with ST production, was a 7.2-kb transcript. Functional inactivation of the gene encoding the 7.2-kb transcript blocked production of ST and all ST intermediate substrates but did not affect transcription of the pathway genes, indicating that this gene was involved in a very early step of ST biosynthesis. These results also indicate that PKSst was not associated with activation of other ST genes. Sequencing of the region spanning this gene revealed that it encoded a polypeptide with a deduced length of 2,181 amino acids that had high levels of similarity to many of the known polyketide synthases and FASs. This gene, pksST, encodes a multifunctional novel type I polyketide synthase which has as active sites a beta-ketoacyl acyl carrier protein synthase, an acyltransferase, duplicated acyl carrier proteins, and a thioesterase, all of these catalytic sites may be multiply used. In addition, a 1.9-kb transcript, which also showed developmental expression, was mapped adjacent to pksST, and the sequence of this gene revealed that it encoded a cytochrome P-450 monooxygenase-like peptide.

[Investigation on invasion of preepiglottic space by supraglottic carcinoma]

This study, based on analysis of 100 whole-organ serial sections of the larynx, concluded that preepiglottic space invasion is involved in 60% of supraglottic carcinoma. The preepiglottic space is involved either by invasion through the adjacent structures of the epiglottis, or more frequently by destroying the epiglottic cartilage and the thyro-epiglottic ligament. The preepiglottic space is involved mainly by epiglottic and epiglottic-ventricular carcinomas, accounting for 95% of carcinomas which invade the space. The involvement of preepiglottic space by supraglottic carcinoma is intimately related to the morphologic features, marginal growth patterns, and T classification. Ulcerative carcinoma is the commonest, accounting for 65%. The incidence of the infiltrative carcinomas is the highest. With increase in T stage, the percentage of invasion of preepiglottic space is increased. We believe that the easy invasion of the preepiglottic space by the supraglottic carcinoma is due to the fact that the epiglottic and epiglttic-ventricular carcinomas which account for 83% of supraglottic carcinomas are located in front of the larynx. In addition, the carcinoma easily destroys the epiglottic, cartilage and enters the preepiglottic space because the embryonic barrier which exists below the glottis and the perichondrium of the epiglottic cartilage is quite fragile.

Polymeric 6-aminoquinoline, an activated carbamate reagent for derivatization of amines and amino acids by high-performance liquid chromatography

A new polymeric reagent containing the 6-aminoquinoline (6-AQ) tag was developed and applied for the off-line derivatization of amines and amino acids in high-performance liquid chromatography (HPLC). The synthesis and characterization of this polymeric reagent are described. An authentic external standard of a typical amine was synthesized and characterized for the determination of the derivatization efficiency. All amines had a derivatization efficiency higher than 50%; the derivatization of amino acids was performed under optimized phase-transfer catalysis reaction conditions. Derivatized amines and amino acids were separated under conventional reversed-phase conditions and determined by UV and FL detectors. To investigate the practical applications, this polymeric reagent was also used to derivatize protein hydrolysates.

[The inhibitory effect and its mechanism of transferrin on FSH-induced differentiation of granulosa cells]

Transferrins are a class of related metal-binding transport glycoproteins for transporting iron to various organs and tissues of the body. In recent years, it has been reported that the transferrin can play an important role in the local regulation of ovarian function, apart from its iron-binding characteristic. Transferrin could attenuate FSH-induced differentiation of rat and human granulosa cells and its mechanisms were considered as follows: (1) Transferrins partially blocked the binding of FSH with its receptors on granulosa cells and reduced the formation of intracellular cAMP, and therefore inhibited the expression of FSH receptors. (2) Acting sites beyond cAMP formation also existed for the inhibitory effect of transferrin on inhibin and estradiol production. (3) The inhibitory effect of transferrin seemed not to be involved in the changes of protein kinase C activity, the calcium release and "proliferation-differentiation reversed mechanism" in granulosa cells.

Nucleotide sequence of the gene encoding the Corynebacterium glutamicum mannose enzyme II and analyses of the deduced protein sequence

The complete nucleotide sequence of the gene encoding the Corynebacterium glutamicum mannose enzyme II (EIIMan) was determined. The gene consisted of 2052 base pairs encoding a protein of 683 amino acid residues; the molecular mass of the protein subunit was calculated to be 72570 Da. The N-terminal hydrophilic domain of EIIMan showed 39.7% homology with a C-terminal hydrophilic domain of Escherichia coli glucose-specific enzyme II (EIIGlc). Similar homology was shown between the C-terminal sequence of EIIMan and the E. coli glucose-specific enzyme III (EIIIGlc), or the EIII-like domain of Streptococcus mutans sucrose-specific enzyme II. Sequence comparison with other EIIs showed that EIIMan contained residues His-602 and Cys-28 which were homologous to the potential phosphorylation sites of EIIIGlc, or EIII-like domains, and hydrophilic domains (IIB) of several EIIs, respectively.

Nucleotide sequence of the pectate lyase gene from alkali-tolerant Bacillus sp. YA-14

The nucleotide sequence of the pectate lyase gene (pe lK) from alkali-tolerant Bacillus sp. was identified and analyzed. A 1,260-base pair open reading frame for the pe lK gene was observed and encoded for a protein of 420 amino acids. The signal peptide was composed of 21 amino acid residues. In the deduced primary structure of this enzyme, the three conserved regions of several pectate lyases were found and showed high homologies.

Purification and characterization of alkaline serine protease from an alkalophilic Streptomyces sp

SAP, an extracellular alkaline serine protease produced by Streptomyces sp. YSA-130, was purified to homogeneity by CM-Sephadex column chromatography and crystallization. The enzyme was a monomeric protein with a molecular weight of 19,000 as estimated by SDS-PAGE and gel filtration. The amino acid composition and amino-terminal sequence of SAP were similar to those of other bacterial serine proteases, i.e., Streptomyces griseus proteases A and B, Lysobacter enzymogenes alpha-lytic protease and Nocardiopsis dassonvillei subsp. prasina OPC-210 alkaline serine protease NDP-I. The optimum temperature and pH for the enzyme activity were 60 degrees C and 11.5. The enzyme was stable up 50 degrees C, and between pHs 4 and 12. The activity was inhibited by Ag+, Hg2+, Co2+, sodium dodecyl sulfate. N-bromosuccinimide, diisopropyl phosphorofluoridate (DFP), 2,3-butanedione, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), iodoacetate, N-ethylmaleimide (NEM), phenylmethanesulfonyl fluoride (PMSF), and phenylglyoxal.

[Haemorrheological effects of different processed products of radix Aconiti Kusnezoffii on animal model with syndrome of "accumulation of cold and blood stasis"]

The effects of Radix Aconiti Kusnezoffii processed by moistening in combination with steaming method and by pharmacopoeial method as well as of the crude drug on haemorrheological nature and the plasma fibronogen content and platelet aggregation rate in the rat model with syndrome of "accumulation of cold and blood stasis" were studied, the result shows that the product processed by moistening in combination with steaming works best.

Antihyperglycemic action of guanidinoalkanoic acids: 3-guanidinopropionic acid ameliorates hyperglycemia in diabetic KKAy and C57BL6Job/ob mice and increases glucose disappearance in rhesus monkeys

To evaluate the long-held concept that acidic guanidines lack glycemic effects, guanidinoalkanoic acids and the biguanide metformin (positive control) were administered to KKAy mice, a model of noninsulin-dependent diabetes. Two acidic guanidines, 3-guanidinopropionic acid (3-GPA) and guanidinoacetic acid, decreased the plasma glucose level; other compounds were ineffective. 3-GPA was more potent than even metformin. Insulin suppression tests in KKAy mice indicated that improved insulin sensitivity was the mode of action for 3-GPA. Glycemic effects in KKAy mice resulted from increased glucose disposal whereas gluconeogenesis, hepatic glycogen content and intestinal glucose absorption were unchanged. 3-GPA's glycemic effect was corroborated in two other models of noninsulin-dependent diabetes. In ob/ob mice, the compound reduced hyperglycemia, polyuria, glycosuria and hyperinsulinemia. In insulin-resistant rhesus monkeys, it increased the disappearance of i.v. glucose. The glycemic action of 3-GPA required the presence of some circulating insulin as well as hyperglycemia because the compound was ineffective in normoglycemic mice, insulinopenic Chinese hamsters and streptozotocin-diabetic rats. These data indicate that acidic guanidine derivatives can ameliorate hyperglycemia in animal models of noninsulin-dependent diabetes. Because acidic derivatives uniquely lack the propensity of guanidine compounds for inducing lactic acidosis, our finding suggests a new approach for developing improved antidiabetes compounds from this chemical class.

An insert of seven amino acids confers functional differences between smooth muscle myosins from the intestines and vasculature

The molecular mechanisms underlying the heterogeneity in contractile properties observed among smooth muscle tissues are unknown. We examined whether part of this diversity might be intrinsic to myosin by comparing structural and enzymatic properties of myosins from two physiologically diverse tissues. Using the reverse transcriptase polymerase chain reaction, we compared avian intestinal smooth muscle and vascular smooth muscle myosin heavy chain (MHC) mRNA. We found that intestinal, but not vascular, MHC mRNA contains an insert of 21 nucleotides, encoding 7 amino acids, in a region near the ATP binding site in the myosin head. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of purified myosin revealed that the relative mobilities of the previously described intestinal MHC isoforms SM1 (204 kDa) and SM2 (200 kDa) were slower than the corresponding vascular SM1 and SM2 isoforms. Furthermore, antibodies raised against a synthetic peptide corresponding to the deduced amino acid sequence of the intestinal insert strongly recognized intestinal SM1 and SM2 but only weakly recognized the vascular isoforms. The presence of the insert in intestinal myosin correlated with a higher velocity of movement of actin filaments in vitro and a higher actin-activated Mg(2+)-ATPase activity, compared with vascular myosin. Other than the MHC insert, one other structural difference distinguished intestinal and vascular myosins: two isoforms of the 17-kDa myosin light chain were found in vascular myosin, whereas a single isoform was found in intestinal myosin. Exchange of the intestinal myosin light chains onto the vascular MHC did not alter its activity in the in vitro motility assay, suggesting that the 7-amino acid MHC insert is responsible for the different enzymatic activities of vascular and intestinal myosins.

Effects of clonidine on the calcium content and morphology of rat salivary glands

These effects were examined with and without pretreatment of animals with reserpine and the adrenergic antagonists prazosin (alpha 1), yohimbine (alpha 2) and propranolol (beta). The effects of clonidine on glandular concentrations of norepinephrine and dopamine also were examined. These effects were compared with those of xylazine, a presynaptic alpha 2-adrenergic agonist. A single, high dose of clonidine followed by an overnight fast caused marked increases in calcium content and acinar secretory granules in the submandibular and sublingual glands, similar to those caused by reserpine. However, the calcium content of the parotid gland was not altered by clonidine, although there seemed to be a modest increase in acinar secretory granules. The clonidine-induced increase in submandibular calcium content could not be attributed to any adrenergic receptor activity since it was not blocked by either alpha- or beta-adrenergic antagonists. Unlike reserpine, clonidine did not affect catecholamine concentrations in the parotid and submandibular glands. Pretreatment with reserpine did not significantly alter the clonidine-induced increase in submandibular calcium content. It is likely that the greater accumulation of acinar secretory granules is related to the increased calcium stores of the glands in clonidine- and/or reserpine-treated rats. The large differences in calcium content among the three glands might be attributable, in part, to differences in the calcium-binding capacity of their secretory granules. Possible mechanisms for the clonidine effects on salivary-gland calcium include disturbances in membrane-associated pools or gating mechanisms for calcium, which need further study.

[Inhibitory effect of transferrin on the binding and maintenance of FSH receptors in rat granulosa cells]

It has been recently demonstrated that transferrin (TRF) can inhibit the functional differentiation of rat granulosa cells, but the mechanism remains unknown. In present experiment, the effect of TRF on the binding of 125I-rFSH to receptors and on the maintenance of FSH receptors in granulosa cells from immature, diethylstilbestrol treated rats were studied. The results show that the physiological range of TRF partially blocked the binding of 125I-rFSH to granulosa cells in a dose-dependent manner. TRF also dose-dependently inhibited the maintenance of FSH receptors in accordance with the reduced production of progesterone and estradiol. In view of the present and our previous investigation, it could be concluded that mechanisms of the inhibitory effect of TRF on the functional differentiation of granulosa cells mainly involve blockade of FSH binding to its receptors and inhibition of FSH receptor maintenance by FSH.